I was driving to church one Sunday evening in heavy traffic. When I came a few driveways before the church's parking lot, I activated my turn signal, applied the brakes, and turned into the parking lot. I was startled to hear a horn blow from the car behind me. It was odd that I hear any horn in my city, other than a general chorus of car alarms that go off on windy days.
When the service ended, I went out and put my foot on the brake. It was dark, so I would have been able to see the brake lights glowing. But there was a problem -- no lights. I got down on the floor and pushed the brake switch with my fingers. The tail lights lit up like a Christmas tree. But when I pushed the pedal, no lights.
I drove home (carefully) and disassembled the assembly. With my ohm meter I measured and found it working with minimal resistance. I grounded the brake wires and found the lights were working. I put it back together and again found that they did not light up.
It turns out that the switch was bad, but only when pushed at the right angle and with the right pressure all while mounted in the brake pedal frame. A $20 switch at the dealer solved the problem.
This entry was submitted by John Bate and edited by Jennifer Campbell.
John Bate has been a system engineer at Volvo Trucks since 1999, working with electrical harness design and process improvement. His background includes embedded computers and software, HF radio design, telematics, and writing copious amounts of simulation models and processes improvement software.
Tell us your experience in solving a knotty engineering problem. Send to Jennifer Campbell for Sherlock Ohms.
William K: I have to disagree with you there. For one thing, there are at least 50 microcontrollers in a car today. It is often much simpler to put in another microcontroller than trying to integrate software within a central processing unit. Since many of the components come from other manufacurers, or even other divisions of a car company, this makes sense. As for cost, even simple electromechanical are very expensive. My wife and I recently replaced the automatic door lock actuators in a minivan. I think they were between $50 and $100 apiece. And we installed them outselves. I was a fun project. On the other hand, these were simple relays. There are many reasons for the high cost of automotive parts, but not having access to the code is not one of them.
It is almost always "easier" to stick in a micro controller and put in some code than to do any actual engineering. No question about that. BUT the unintended consequences of code that it is unable to handle exceptions, or does not handle the way some users think, and is generally not exactly the best choice. That is the fundamental flw that I see in using software to implement many functions. Primarily code is only written to handle what the programmer believes will happen, which is usually a very small subset of the real world.
Here's a counter to your proposal for using inexpensive microcontrollers....
We were driving our 2000 Pontiac Montana minivan one day when somebody started flashing their lights at us from behind. We asked what was the matter and they said our brake lights were out. That was strange...in 40 years of working on cars, I had never had BOTH lights go out at the same time. Funny thing is that the high-mounted center brake light still worked.
I replaced the bulb on the right side and...NOTHING!!! Same on the left. We called the dealer and they laughed saying, "Oh that must be the controller board." Funny thing that, for over 50 years, a switch was good enough for controlling brake lights, but NOW you need a controller.
Back in the 1990's (I think) Chrysler wired their stereo's into the vehicle's CAN bus. Problem with that was that when the radio failed, the whole vehicle shut down and needed a tow back to the dealer. Seemed like a good idea at the time.
Not only is it harder for DIY auto repair because of the proprietary nature of the components, but because these components interact in complicated ways.
Only legislation requiring manufactures to publish technical spec's on their components (and their component's intended/expected behavior) will improve the situation for the consumer. Thankfully we have the internet and youtube.
I was a comfirmed DIY for years. Points & plugs every 12,000 miles. Oil every 3 and filter every other change. Air filter at 12,000 when the plugs got changed, etc. We do not have to do that junk nearly as often any more. So the brake light switch went bad, big deal. Both mechanical and elecrical parts fail on occasion, and need replacing.
Autos are so much more dependable than years past that when something does go wrong it is worthy of a magazine article. It wasn't that terribly long ago that a vehicle with 75,000 miles on it was almost always ready for the salvage yard. I have fond memories of my first decent car, 1962 Buick with a 401 cubic inch engine,and AFB carb. I would love to have it back. But, I would not want it as my primary mode of transportation, because I am no longer willing to spend every other weekend working on a car. Or at least that is what it seemed like.
I agree. What's the big deal? Finding and replacing a bad brake-light switch doesn't require too much diagnostic effort.
On the other hand, it did get us all started writing these silly messages that we enjoy so much! Thanks, John.
One thing that puzzles me is why a Volvo engineer would write about replacing a bad switch. Certainly there must be something more interesting in his work that would be more interesting to readers as well, but maybe Volvo won't let him publish.
More legislation we do not need. Speak with your wallets! Don't buy cars you don't like because you can't easily service them yourself, or because parts are too expensive.
Mounting a PCB directly against a metal housing, with only solder mask as insulaiton is a bad, bad idea from a reliability perspective. All it takes is a pinhole or crack in the solder mask, and a little corrosion (or a little whisker/dendrite), and a short will develop. Thermal expansion/contraction could also eventually scuff through the solder mask. Space the board off the housing or use robust insulation.
More than one person has tried to mount a computer motherboard directly into a computer case with no standoffs. Guess what happens!
As a closet libertarian it pains me to say, but yes Virginia, we need more legislation to protect the consumer. Car companies do the things they do to maximize profits for their shareholders and stakeholders (dealerships). Then they worry about the labor unions. Customers come last. In a cut-throat environment like the auto industry, there are NO new cars that I know of that are easily/cheaply servicable any more. Certainly such creatures (even if they did exist) wouldn't inspire a blog post here (an example of what you won't read here: "I changed my spark plugs last week, I could reach them all w/o lifting the engine or contorting my body, and it took 15 minutes", yawn.) I would interested to hear any examples of cars that are easy/cheap to service.
But, as an example of "good" legislation: look at the OBD ports in ALL modern cars. Such a thing would NEVER have existed without that legislation. In any case, legislation evens the playing field and allows/forces car companies to do the right thing without going bankrupt.
Critic: You are correct and seldom do all the comments pertain directly to the original post. I learn things from some of the splinters and that makes these forums enjoyable. I guess my gripe was that when something fails it is not always a mistake. Sometimes things just wear out from repeated use and few of us would be willing to pay the price of a vehicle in which everything is built to last through eternity, even if that was possible.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
1 
